Copying machines



Q1 MW Sept. 6 1955 Filed April 4, 1952 F. w. WHITEHEAD 2,716,924

COPYING MACHINES 6 Sheets Sheet 1 fly. 1

' mub ii Sept. 6 1955 F. w. WHITEHEAD 2,716,924

COPYING MACHINES Filed April 4, 1952 6 Sheets-Sheet 2 Sept. 6 1955 F. w. WHITEHEAD 2,716,924

COPYING MACHINES Filed April 4, 1952 6 Sheets-Sheet 3 P 6 1955 F. w. WHITEHEAD 2,716,924

COPYING MACHINES P 6 1955 F. w. WHITEHEAD 2,716,924

I COPYING MACHINES Filed April 4, 1952 6 Sheets-Sheet 5 Sept. 6 1955 Filed April 4, 1952 P0 E4 F F. W. WHITEHEAD COPYING MACHINES 6 Sheets-Sheet 6 United States Patent 6 COPYING MACHINES Frederick William Whitehead, Bristol, England, assignor to The Bristol Aeroplane Company Limited, Bristol, England, a British company Application April 4, 1952, Serial No. 280,549

Claims priority, application Great Britain April 12, 1951 17 Claims. (Cl. 90-13) This invention concerns copying machines and relates more particularly to machines for producing blades or vanes for axial-flow compressors and for turbines and the like. The blade or vane may be rough or finish shaped by the machine and the machine may work on a partly formed blade or vane (e. g. forged or stamped to approximate size) or on a blank or workpiece not previously shaped.

The invention is concerned with copying machines of the type in which a master (whose shape is to be reproduced on a workpiece) engages a guide member and is "Free her and the master and by supporting the master as set T forth, it is ensured that variations in radius from the axis not necessary, as has hitherto commonly been the case, to

manufacture blades or vanes of a shape which is a compromise between that required by the designer and that which enables rapid production to be achieved. The ability rapidly to reproduce the blades or vanes to the designers requirements is of particular importance when the blades or vanes are to be used in gas turbine engines since small departures in shape from the design form may have cumulative effects and may therefore seriously reduce the overall efficiency of the engine. Hitherto blades or vanes have been accurately and rapidly produced by stamping but, due to the high degree of accuracy called for, the dies have a short life and such methods of manufacture are inapplicable where a large number of blades is to be cheaply produced.

The present invention enables blade or vane blanks to be shaped roughly to size by stamping and subsequently accurately machined to size whereby rapid and cheap production is possible.

of oscillation of the master to the surface thereof are explored as the master is moved through the cutting range and that such variations result in the master being pivotally adjusted. Similarly, variations in the inclination of the surface of the master relatively to the-axis of oscillation are explored during the traversing movement and such variations again result in pivotal movement of the master. It will be appreciated that either or both of said variations may be present and that these will be detected and produce a corresponding pivotal adjustment of the master. The pivotal adjustments of the master with oscillation thereof and during the traversing movement are applied to the workpiece while it is similarly oscillated and traversed whereby the workpiece accurately reproduces the movements of the master. I

According to an independent feature of the present invention when the copying machine is to be used for reproducing on a workpiece a convex surface of the master there is provided a circular ring tool having an internal working face or edge of a radius equal to or greater than the maximum radius of curvature of the convex surface to be formed on the workpiece. Alternatively, according to another feature of the invention, the convex surface of a master is reproduced on a workpiece by a circular tool having an external working face to engage the workpiece and reproduce said convex surface.

The invention also finds application to a copying machine of the type set forth for reproducing on a workpiece a concave surface of the master and according to a further feature of the present invention such a machine comprises a guide member to make local engagement with According to a feature of the present invention the copying machine comprises a guide member to make local engagement with the master, a tool similarly to engage the workpiece, means for oscillating the master and workpiece together about parallel axes through the cutting range, means for supporting the master and workpiece for pivotal movement about a common axis normal to the axes of oscillation to move both said axes towards or away from the guide member and tool, the arrangement being that oscillating movements of the master resulting in pivotal movements thereof produce corresponding pivotal movements of the workpiece, and means for moving the master and workpiece relatively to the guide member and tool respectively whereby the master and workpiece are traversed across the guide member and tool generally in the direction of the axes of oscillation. By local engagement is meant engagement over a length considerably smaller than the extent of the cutting range and also of the movement of traverse, i. e. engagement takes place over a relatively small area comparedwith the total area of the surface of the master and workpiece.

By providing local engagement between the guide memthe master, a circular tool having an external working face of a radius not greater than that of the minimum radius of curvature of the concave surface to be formed on the workpiece similarly to engage the workpiece, means for oscillating the master andv workpiece about parallel axes through the cutting range, means for supporting the master and workpiece for pivotal movement about a common axis normal to the axes of oscillation to move both said axes towards or away from the guide member and tool, the arrangement being that oscillating movements of the master resulting in pivotal movements thereof produce corresponding pivotal movements of the workpiece, and means for moving the master and workpiece relatively to the guide member and tool respectively whereby the master and workpiece are traversed across the guide member and tool generally in the direction of the axes of oscillation. A copying machine as set forth may also be utilised for reproducing on a workpiece a convex surface of the master as referred to above. It is therefore possible with a minimum of adjustment and alteration of the machine, to use the same tool to reproduce concave and convex surfaces.

It is common in copying machines continuously to rotate the master and workpiece in one direction. When blades or vanes are to be reproduced by a machine such an arrangement would result in considerable waste of time in the machining operation since the chordwise extent of the blade or vane is, in most cases, relatively small compared with the circumference of the circle of rotation. By providing that the master and workpiece are oscillated instead of rotated the machining time is reduced substantially to a minimum.

Two practical constructions of the invention will now be described, by way of example only, with reference to a machine for shaping turbine blades of gas turbine engines. The description will be made with reference to the accompanying drawings whereof:

Figure 1 'is' a diagramnialic plan view of one construction of machine,

Figure 2 is a view showing to a larger size part of the machine of Figure 1,

Figure 3 is a view in the direction of the arrow 111 of Figure 2,

Figure 4 is a section on the line IV-lV of Figure 2,

Figure 5 is a diagrammatic side elevation, partly in section, showing a modified detail of construction of the machine of Figures 1 to 5,

Figure 6 is a diagrammatic view of a machine for shaping a plurality of turbine blades at the same time using a single master, and

Figure 7 is a view in the direction of the arrow VII of Figure 6.

Referring to Figures 1 to 4: the machine is adapted to reproduce on a workpiece the convex surface of a master blade. The machine comprises a base 10 on which are mounted a toolhead assembly ill, a guide member assembly 12 and an assembly 13 carrying the master 14 and the workpiece 15 for oscillation through the cutting range and for movements of traverse relatively to the other two assemblies, the master being associated with the guide member assembly and the workpiece with the toolhead assembly. The assembly 13 is shown in Figure l as mounted on slides 16 for traverse towards and away from assemblies 11 and 12 and there is shown a handwheel 17 for traversing the assembly 13 in well known manner. The handwheel may be replaced by a suitable power drive.

The assembly 12 comprises a block 18 bolted to base 10 and supporting a spindle 19 one end of which carries a guide member 20 which in the present instance is a disc, the peripheral edge 21 of which engages the master 14 as later described.

The toolhead assembly 11 comprises a bearing block 22 bolted to the base 10 and. supporting a shaft 23 which is driven in any known or convenient manner e. g. through gear box 24 from an electric motor 25. The shaft 23 carries a cylindrical milling cutter 26. The axes of shafts 19, 23 are parallel. The milling cutter engages the workpiece 15 as later described.

The assembly 13 which supports the master 14 and the workpiece 15 comprises a bearing block 27 which is carried by a saddle 28 supported from the base 10 for reciprocating movement towards and away from the guide member and the milling cutter as described above.

The bearing block 27 supports a shaft 29 Which is capable of rotation about a horizontal axis x and there is mounted at each end of the shaft a holder 30, one of which is provided to support the master 14 and the other of which is provided to support the workpiece 15. The holders for the master and the workpiece are of similar construction and for convenience therefore only one will be described in detail hereinafter and it is sufficient to state at this point that the master and workpiece are supported by the holder in bearings 31 (carried by shaft 29) for oscillation about axes y i. e. normal to the pivotal axis x of the holder. tion are generally parallel to the axes of shafts l9 and 23. The oscillation of the master and of the workpiece is suitably limited and preferably is slightly in excess of the maximum total of angle of twist of the blade.

The holders for the master and the workpiece each carries a pin 32 which is offset from the axis y and the pins are coupled together by a connecting rod 33 so that the master and the workpiece oscillate together (Figure 4). in the preferred arrangement the holders are each provided with a plate 34 from which said pin projects and the connecting rod incorporates a turnbuckle 35 whereby the length of the rod may be adiustable to vary the relative settings of the master and workpiece about their axes of oscillation.

A pn umatic jack 36 is provided, the piston 3'? of which is connected with the plate 34 associated with the workpiece holder, the jack being suitably supported The axes of osciila-.

from one of the bearings 31 (Figure 2). The jack is such that when compressed air is supplied to it the workpiece holder will be oscillated in one direction or the other and such movements are transmitted through the connecting rod to the holder for the master.

The holder plate 34 for the master is provided with a pair of stops 38 which are angularly adjustable, along slot 39, and about the axis y of oscillation to vary the distance between them. A switch lever 40 is pivotally mounted, at 41, on one of bearings 31 and has one arm lying between the stops and the other arm arranged to operate a microswitch 42 carried by bearing 31. The microswitch is in the circuit (not shown) of a solenoid provided to control, in one direction only, a valve which I regulates the passage of compressed air to the pneumatic jack, the valve being re-set by a spring when the solenoid is deenergised.

With the arrangement described, when the master 14 has been oscillated through the cutting range in one direction one of the stops 33 engages lever 43 to actuate the microswitch 42 whereby the supply of compressed air to the jack is reversed. The master is therefore oscillated in the opposite direction until the other stop 38 engages said lever 40 whereupon the jack is again reversed. It will be seen therefore that the oscillating movements of the master and jack proceed automatically. The stops are angularly spaced so as to provide the required maximum total angle of twist referred to above.

The master is adapted to engage the lower part of edge 23 of member 20 and being pivoted about axis x is capable of adjustment in a vertical plane. The workpiece is adapted similarly to engage the milling cutter 26. The master is kept in contact with the edge 21 of the guide member 20 and the workpiece in contact with the milling cutter 26 by tension springs 43 (Figure 3) and there is provided a threaded spindle whereby the tension may be released when the machine is being set up prior to the milling operation on the workpiece so that the master and workpiece may be brought into engagement with the guide member 20 and the milling cutter respectively as mentioned above and thereafter the spring tension is applied to maintain said engagement. Alternatively, a spring plunger may be provided to hold the master and the workpiece downwardly tilted and clear of the guide plate and milling cutter, the plunger being manually brought into use when required.

Each holder 30 comprises a shaft 44 to be received by its bearing 31 for rotation in the bearing about the axis y. One end of shaft 44 carries a platform 45 to which the master or workpiece is removably attached and the other end projects from the shaft bearing and receives the plate 34 which carries the connecting pin and stops mentioned above. The platform 45 extends in the lengthwise direction of the master and is formed with a surface suitably shaped to receive and support the master, or workpiece which is clamped to the platform so that it is incapable of movement on the platform during the copying operation.

To remove one blade blank from its holder and replace it by another it is only necessary to unfasten the clamping means and thereafter tighten said means when the new blade blank has been mounted with its concave face suitably supported on the platform.

In use, a master having the required shape of the convex surface which is to be reproduced on the workpiece is attached to its holder 30. Thereafter a blade blank having the approximate shape of the blade as produced by a stamping operation is mounted in the workpiece holder after the length of the connecting rod 33 has been suitably adjusted by the turnbuckle 35 to bring the master holder and the workpiece holder into correct angular relationship about their axes of oscillation y and after the stops 38 have been adjusted so that the master and Workpiece holders can swing through the required cutting range.

The tension of the spring 43 is then released and the saddle 28 is moved forward whereby the tip of the master 14 and of the workpiece 15 are brought beneath guide member and milling cutter 26. The saddle is adjusted as described either manually or by the automatic feed of the machine. Tension is then applied to spring 43 whereby the master and the workpiece are brought into engagement with the guide member 21 and with the milling cutter 26 and kept in contact therewith by the tension of the spring. The air supply to the control valve for the pneumatic jack 36 is then turned on and the milling-cutter motor is started.

As indicated above the workpiece and the master are oscillated together and in synchronism, the extent of oscillation being limited by the stops and the reversals in oscillation being automatically performed under the control of the microswitch. Simultaneously the saddle is moved forward either manually or automatically i. e. towards the milling cutter and the guide member so that the master and the workpiece perform a traversing movement. The traversing movement is continued until the whole of the length of the blade has been machined, during which time the master passes entirely across the guide member and the workpiece passes under the milling cutter.

Variations in the radius from the axis of oscillation of the master to the convex surface are explored by member 20 as the master is moved through the cutting range and traversed and such variations produce corresponding pivotal movements (about axis x) of the master which are applied to the workpiece. The surface of the master is therefore accurately reproduced on the workpiece by the milling cutter.

When the convex face of the workpiece has been fully machined the saddle is withdrawn, the workpiece removed and replaced by another blank and thereafter the sequence of operations described above isrepeated.

The guide member 20 may be supported on the block 18 for limited lateral movements and means are provided for so adjusting the member. The spring which holds the master against the guide member 20 applies the workpiece to the milling cutter so that the machining operation on the workpiece is performed and the depth of cut is determined by laterally adjusting member 20. This means that the workpiece is engaged with the millingcut. ter by the spring before the master engages the guide member and removal of metal from the workpiece by the milling cutter enables the master to engage the guide member and determine the shape being reproduced by the milling cutter.

There is diagrammatically shown in Figure 5 a modification of the machine described above wherein the guide member comprises a disc having a circular opening to receive the master 14--the latter being supported as previously described with reference to Figures 1 to 4..

An internal milling cutter 51 is provided to shape the workpiece 15 which is mounted as described above. internal milling cutter is suitably driven in any known or convenient manner. The master 14 is adapted to engage the top of the hole in the guide disc 50 and the workpiece 15 is adapted similarly to engage the top of the milling cutter 51. The arrangement described is provided for reproducing a convex surface on the workpiece 15. The milling cutter 51 has an internal radius equal to or greater than the maximum radius of curvature which has to be cut on the convex face of the workpiece. The circular opening in the guide disc or ring 50 has the same internal radius as the milling cutter 51. With the arrangement shown in Figure 5 a single milling cutter may be used with a large number of different shapes and sizes of blades provided that the internal radius of the cutter fulfills the above requirements in all cases.

For reproducing the concave surface of a master on a workpiece the machine described above with reference to Figures 1 to 4 is used, it being ensured that the cutter Thehas a radius which is not greater than that of the mini-- mum radius of curvature of the surface to be formed.

on the workpiece and the diameter of the guide disc is equal to the diameter of the milling cutter.

by a grinding wheel or by a single point tool.

In order to enable a large number of blades to be rapidly. produced, it is preferred to reproduce the concave or convex surface of a master on a plurality of workpieces at the same time. A machine for doing this is illustrated in Figures 6 and 7 to which reference will now be made. In Figure 7 the parts encircled in Figure 6 have been omitted to show the master, master holder and the guide member. 1

The machine comprises a bed 60 within which is mounted an electric motor 61 which drives six vertical.

spindles 62 by belts 63. Centrally mounted between two groups of three spindles is a holder which carries a master 55, the surface of which is to be reproduced as later described. The holder 64 is capable of oscillation about a vertical axis v, the holder being supported in a bearing member 65 for this purpose. The bearing member 65 is supported by bearings 66 for movement about the horizontal axis h. The assembly comprising the bearing member 65 and the bearings 66 is carriedby a frame 67 which is mounted on slides 68 for vertical movement, 7 the weight of the assembly 65, 66, 67 being counterbalanced by weights, the assembly and the weights being connected together by cords The member 65 carries a plurality of depending discs 71 to each of which may be attached a holder to carry a workpiece.

The master holder 64 is oscillated by a shaft 72- which is driven through bevel gearings 73. An electric motor 74 drives through gear box 75 a shaft'76 carrying a crank The crank 77 is coupled. with a crank 78 drivingly connected with the bevel wheel 77 whose throw is adjustable.

73 by means of a connecting rod 79, the arrangement being that the motor 74 oscillates the bevel gear 73 and hence the master holder 64. The bevel gear 73 is mounted on a shaft 80 extending across the member 65 and carrying bevel gears 81, one for each depending disc 71. Each disc 71 is mounted on a shaft which carries a bevel pinion 82 to mesh with one of the gears 81. In this way each of the discs 71 will be. oscillated in the same fashion as the master holder 64 and as the workpieces 88 are carried in work holder 89 by the discs 71 it follows that,

;master 55.

The member 65 has a pair of upwardly extending arms 83 and each arm is coupled to a pair of springs 84 which are anchored to the arm 67, the springs being sufliciently strong, when the machine is in use, to hold the master 55 in engagement with a guide member 85 in the form of a circular disc. The member 65 is also provided with an arm 86 between which and the arm 67 there is located a pneumatic jack 87. When compressed air is supplied to the jack 87 the member ofthe springs 84 to carry the master 55 guide 85.

Each of the spindles 62 is adapted to carry an external milling cutter 56, the diameter of which isthe same as the diameter of the guide disc 85, and each milling cutter 56 is adapted to engage the workpiece 88 which is supported by the work holder 89 immediately above the corresponding spindle 62.

The machine also incorporates any known or convenient mechanism for raising and lowering the frame 67 either manually or automatically so that the master 55 is traversed across the guide 'disc 85 and at the same time the workpieces 88 are carried across the milling cutters 56. Simultaneously the master 55 and the workpieces 88 are oscillated. Since the master and the workpieces are capable of oscillation about horizontal axis h, variations away from the 69 passing over pulleys 70.

65 is rocked against the action in the radius from the axis of oscillation of the master to the convex surface thereof are explored by the guide disc 85 as the master is moved through the cutting range and travels as described above. Such variations produce corresponding pivotal movements of the member 65 about the axis h. and these are applied simultaneously and to the same extent to all the workpieces carried by the work holders 89. The surface of the master is therefore accurately reproduced on each of the six workpieces by the milling cutters. When the workpieces have been shaped the pneumatic jack 87 is brought into operation to adjust the member 65 against the action of the springs 84 whereby the master 55 is moved away from the guide disc 85 and the workpieces are moved away from the milling cutters so that access may be had to the workpieces for removal and replacement. Prior to the commencement of a new copying operation the frame 67 will be raised so that the cycle of operations detailed above will again be carried out.

The present invention has particular application to machines for producing blades for compressors and turbines but it will be appreciated that it has other applications where a convex and/or concave surface disposed transversely to a long axis is to be accurately, rapidly and cheaply produced.

I claim:

1. A copying machine of the type set forth comprising a base, a guide member carried from the base and fixedly located relatively to the base to make local engagement with the master, a tool carried from the base and fixedly located relatively to the base similarly to engage the workpiece, means for continuously oscillating the master and workpiece together about parallel axes through the cutting range, said parallel axes lying generally in the plane containing the long axes of the master and workpiece, means for supporting the master and workpiece for pivotal movement about a common axis normal to the axes of oscillation to move both said axes towards or away from the guide member and tool, the arrangement being that oscillating movements of the master resulting in pivotal movements thereof produce corresponding pivotal movements of the workpiece, and means for moving the master and workpiece relatively to the guide member and tool respectively whereby the master and workpiece are traversed across the guide member and tool generally in the direction of the axes of oscillation.

2. A copying machine of the type hereinbefore set forth for reproducing on a workpiece a concave surface of the master comprising a base, a guide member carried from the base and fixedly located relatively to the base to make local engagement with the master, a circular tool carried from the base and fixedly located relatively to the base and having an external working face of a radius not greater than that of the minimum radius of curvature of the concave surface to be formed on the workpiece similarly to engage the workpiece, means for continuously oscillating the master and workpiece about parallel axes through the cutting range, said parallel axes lying generally in the plane containing the long axes of the master and the workpiece, means for supporting the master and workpiece for pivotal movement about a common axis normal to the axes of oscillation to move both said axes towards or away from the guide member and tool, the arrangement being that oscillating movements of the master resulting in pivotal movements thereof produce corresponding pivotal movements of the workpiece and means for moving the master and workpiece relatively to the guide member and tool respectively whereby the master and tool are traversed across the guide member and tool generally in the direction of the axes of oscillation.

3. A copying machine of the type hereiubefore set forth for reproducing on a workpiece a convex surface of the master comprising a base, a guide member carried from the base and fixedly located relatively to the base to make local engagement with the master, a circular tool carried from the base and fixedly located relatively to the base and having an external working face similarly to engage the workpiece, means for continuously oscillating the master and workpiece about parallel axes through the cutting range, said parallel axes lying generally in the plane containing the long axes of the master and the workpiece, means for supporting the master and workpiece for pivotal movement about a common axis normal to the axes of oscillation to move both said axes towards or away from the guide member and tool, the arrangement being that oscillating movements of the master resulting in pivotal movements thereof produce corresponding pivotal movements of the workpiece, and means for moving the master and workpiece relatively to the guide member and tool respectively whereby the master and tool are traversed across the guide member and tool generally in the direction of the axes of oscillation.

4. A copying machine of the type hereinbefore set forth for reproducing on a workpiece a convex surface of the master comprising a base, a guide member carried from the base and fixedly located relatively to the base to make local engagement with the master, a circular ring tool carried from the base and fixedly located relatively to the base and having an internal working face of a radius greater than the maximum radius of curvature of the convex surface to be formed on the workpiece similarly to engage the workpiece, means for oscillating the master and workpiece about parallel axes through the cutting range, means for supporting the master and workpiece for pivotal movement about a common axis normal to the axes of oscillation to move both said axes towards or away from the guide member and tool, the arrangement being that oscillating movements of the master resulting in pivotal movements thereof produce corresponding pivotal movements of the workpiece, and means for moving the master and workpiece relatively to the guide member and tool respectively whereby the master and tool are traversed across the tracer and tool generally in the direction of the axes of oscillation.

5. A copying machine as claimed in claim 4 wherein the tool comprises a milling cutter with internal teeth.

6. A copying machine as claimed in claim 5 in which the guide member comprises a ring having the same internal diameter as the internal diameter of the tool, the circular axes of the ring and the axis of rotation of the tool being parallel.

7. A copying machine as claimed in claim 1 wherein the means for oscillating the master and workpiece comprises a reciprocating pneumatic or hydraulic jack the movements of which are applied to the workpiece to oscillate it and means for transmitting the oscillating movements from the workpiece to the master.

8. A copying machine as claimed in claim 7 wherein the transmission means comprises a pair of pins connected one each to the master and workpiece and offset from the axis of oscillation thereof and a rod connecting the pins together.

9. A copying machine as claimed in claim 7 wherein stops are provided to limit the cutting range and electric switch means are provided to actuate means for reversing the jack when a stop is engaged.

10. A copying machine as claimed in claim 1 in which holders are provided removably to carry the master and workpiece, and said holders are supported for oscillating movement in members which are rigidly connected together and are supported by a bearing, disposed between the holders, for pivotal movement of said members.

11. A copying machine according to claim 1 comprising a single master holder and a plurality of workpiece holders drivingly interconnected therewith whereby the shape of a master may be simultaneously reproduced on a plurality of workpieces.

12. A copying machine as claimed in claim ll wherein the master holder and the plurality of workpiece holders are carried by a member mounted to perform said pivotal movements, all said holders being interconnecting to perform said oscillating movements relatively to the frame about parallel axes which are normal to the pivotal axis so that all the holders have the same movement of oscillation.

13. A copying machine as claimed in claim 12 wherein each workpiece holder and the master holder'are connected by gearing with a common cross-shaft mounted on the frame and a motor is provided to oscillate the cross-shaft.

14. A copying machine according to claim 13 in which the holder-carrying member is mounted on a slide movable on the bed of the machine which carries, for each workpiece holder, a tool and for the master holder a guide member the arrangement being that the slide traverses the master and workpieces relatively to the guide member and the tools respectively.

15. A copying machine as claimed in claim 14 wherein the master holder and the workpiece holders are arranged in line, the workpiece holders being on each side of the master holder.

16. A copying machine as claimed in claim 15 in which the tools are external milling cutters allof which are driven by a common motor.

17. A copying machine as claimed in claim 2 in which the guide member comprises a disc having the same diameter as the external diameter of the tool, the circular axis of the disc and the axis of rotation of the tool being parallel.

References Cited in the file of this patent UNITED STATES PATENTS 1,325,671 Heath Dec. 23, 1919 1,503,687 Hunt Aug. 5, 1924 2,005,508 Shaw June 18, 1935 2,125,881 Berliner Aug. 9, 1938 2,178,441 Swanson Oct. 31, 1939 2,335,625 Wilson Nov. 30, 1943 FOREIGN PATENTS 541,342 Great Britain Nov. 27, 1941 

